Communication networks are widely used for transferring data between different systems such as, for example, computer systems and mass storage systems and other peripheral equipment.
In communication networks, when data are transmitted by a transmitting station to a receiving station, a repeater is sometimes required between the transmitting and receiving stations. The repeater may be necessary to boost a signal which must be transmitted over a long distance between the transmitting and receiving stations. In another application, the repeater interconnects two segments of a path having different transmission media, such as optical fiber and copper.
In communication networks, such as FDDI networks, errors present on a link between the transmitting and receiving stations (link errors) are counted by a physical layer device (PHY) in the receiving station. Link errors are encoded with communication symbols which eliminate run length error problems associated with certain link errors. These communication symbols are valid physical layer symbols, and thus the receiving station PHY does not recognize them as violations. These symbols are, however, recognized as violations by the receiving station Media Access Controller (MAC). Thus, when a conventional FDDI station is used as a repeater (FDDI station repeater), FDDI-I and FDDI-II standards are followed to filter a stream of 5-bit symbols that enters the station. Thus, when receiving a frame with a code violation (i.e., operating in basic (FDDI-I) mode), after counting the error, a FDDI station repeater replaces the violation symbols responsible for the code violation with four Halt symbols followed by an Idle line state. This Idle line state is transmitted to a downstream receiving station until the FDDI station repeater receives the next frame of data. When receiving a hybrid cycle with a code violation (i.e., operating in hybrid mode (FDDI-II) mode), after counting the error, the FDDI station repeater replaces the symbol responsible for the code violation with an L symbol. When receiving neither frames nor cycles, code violations are replaced with idle symbols.
A PHY detects a link error when either the current line state is active line state or cycle line state and a V symbol is decoded. This includes receipt of any invalid code point or a J or K which is not decoded as part of a starting delimiter. The PHY also detects a link error when the current line state is idle line state and any symbol except Q, H, I, J or K is decoded. This includes receipt of any invalid code point or a J or K which is not decoded as part of a starting delimiter.
A MAC layer device detects a format error when the MAC is in the process of receiving a frame or token and an error is detected that prevents complete reception. This includes receipt of any non data symbol except T or I (while receiving a frame or token).
Because conventional FDDI station repeaters transfer link errors into symbols which are valid for the PHY in the downstream station, these errors are not detected or counted by the link error monitor present in the PHY of the downstream receiving station. This allows errors to be isolated onto the link on which the errors occurred. This is undesirable in a repeater because the error count in the link error monitor of the PHY in the downstream station is deceptively low, making the link appear to be in a better condition than it actually is. The link error processing is consequently impeded. In addition, the FDDI station repeater is not "transparent" to the transmitting and receiving stations.
It is therefore desirable to have a repeater which will operate transparently. That is, the repeater will transmit violations with minimal filtering so that the PHY in a receiving station will be able to detect link errors that occurred between the upstream station and this station even if repeaters are present in the path. It is also desirable to have a repeater which transmits link error information using communication symbols which do not create run length problems within the receiving station. It is also desirable to have a repeater which can be programmed to operate as either a conventional FDDI repeater or as a "transparent" repeater.
In addition, prior art repeater stations require an FDDI station management entity. It is desirable to simplify repeater stations, and make them faster, by enabling them to operate without station management.